Method of forming a continuous web of uniform thickness by applying reciprocating action to cellulosic fibrous stock in a headbox

ABSTRACT

The present invention relates to a method for forming a continuous web of substantially fibre-containing stock having a consistency in the range of about 6 to 35 percent by applying a reciprocating action to the stock in a headbox to advance the stock onto a forming surface, said reciprocating action providing substantially the sole means causing said stock to flow from said headbox.

United States Patent Inventor Emile A. Cambron Hudson, Quebec, Canada Appl. No. 777,710 Filed Nov. 21, 1968 Patented Nov. 23, 1971 Assignee Domtar Limited Montreal, Quebec, Canada Priority Oct. 21, 1968 Canada 33,147

METHOD OF FORMING A CONTINUOUS WEB OF UNIFORM THICKNESS BY APPLYING RECIPROCATING ACTION TO CELLULOSIC FIBROUS STOCK IN A HEADBOX [56] References Cited UNITED STATES PATENTS 3,562,108 2/1971 Lopas 162/341 1,928,107 9/1933 Lang 162/212 2,904,461 9/1959 Washburn et al [62/344 X 3,298,903 l/1967 Hart 162/236 3,477,905 1l/l969 Rogers 162/336 X FOREIGN PATENTS 560,577 4/1944 Great Britain 162/341 OTHER REFERENCES 162- 341 Search Card Primary Examiner-S. Leon Bashore Assistant ExaminerArthur L, Corbin Attorney-C. A. Rowley ABSTRACT: The present invention relates to a method for forming a continuous web of substantially fibre-containing stock having a consistency in the range of about 6 to 35 percent by applying a reciprocating action to the stock in a headbox to advance the stock onto a forming surface, said reciprocating action providing substantially the sole means causing said stock to flow from said headbox.

PATENTEDHUV 23 I971 INVLNIUR Emile A. CAMBRON METHOD OF FORMING A CONTINUOUS WEB OF UNIFORM THICKNESS BY APPLYING RECIPROCATING ACTION TO CELLULOSIC FIBROUS STOCK IN A HEADBOX The present invention relates to a method and apparatus for the formation of webs, more particularly to the formation of fiber-containing boards from high-consistency stocks.

As is well known, webs such as paper webs or boards are usually formed from relatively low consistency flowable stocks to facilitate forming a sheet with the proper characteristics. With some materials, such as a combination of cellulosic fibers and lightweight mineral aggregates (e.g. expanded perlite), it is necessary to increase the consistency of the forming mixture to prevent separation of the lightweight aggregates from the fibers by flotation. This type of operation uses a consistency of above 3 percent but less than 8 percent and generally about 5 percent. To applicants knowledge, no forming systems are known for laying webs from stocks having consistencies above 8 percent other than dry forming techniques.

It is thus the main object of the present invention to provide a method and apparatus for forming fiber-containing webs from stocks having consistencies in the range of about 6 to 35 percent.

Broadly, the method of the present invention comprises maintaining a pool of high-consistency stock, positively and intermittently displacing said stock at one end of said pool toward the opposite end by a reciprocating action, flowing stock from said pool at the said opposite end of said pool, metering the thickness of the layer of said stock flowing from said pool thereby to form a substantially uniform web of said stock.

The present invention also relates to an apparatus for forming a web and comprising a head box, means to supply highconsistency stock at a controlled rate to said head box, metering means adjacent the outflowing end of said head box, and means to reciprocate the backwall of said head box whereby said stock flows from said head box and forms a substantially uniform web.

Further features, objects and advantages will be evident from the following detailed description taken in conjunction with the accompanying drawings in which:

The drawing is a schematic illustration of the method and apparatus for carrying out the present invention.

The apparatus of the present invention basically includes a mixer 10, a hopper l2, metering valve 14, a reciprocating head box 16 with a driven metering roll 18 at its outlet end and a forming wire 20 to receive the stock flowing from the head box.

The mixer 10 may be any conventional means suitable for mixing the ingredients from which the board is to be formed.

The hopper 12 contains a supply of stock, and the metering valve 14 regulates the amount of stock flowing from the hopper 12 into the head box 16.

The valve 14 may be driven by any suitable means schematically designed by the arrow 13. Preferably sensing means,

such as those schematically illustrated at 22, senses the level L of the pool 17 of stock in the head box 16, and controls the valve 14 to maintain the level L substantially constant as schematically illustrated by the line 23.

The head box 16 is one of the most important elements in the combination forming the present invention. The head box 16 as illustrated may simply be an open box into which the stock from the hopper 12 is dumped. Flow of stock from the head box 16 is obtained by reciprocating at least the rear wall 26 and preferably the whole head box including the rear bottom and sidewalls; with some stocks at high consistency. The required reciprocating action may be obtained by any suitable means as schematically designated by the arrow 25. The bottom of the box may be sloped down toward the outlet end so that the bottom in effect also forms the rear wall of the head box. Such reciprocating movement, it is believed, on the forward stroke positively displaces the stock in the head box toward the outlet end.

The specific amplitude and frequency of the reciprocating motion of the head box is dependent on the feed rate desired and the material being fed. The optimum motion of the head box will vary with resonant frequencies of the specific head box being used. The reciprocating motion is substantially along straight lines rather than on a pronounced elliptical or arcuate orbit so that any point on the reciprocated section of the head box moves in a substantially straight line in one direction during the advancing stroke and in the opposite direction during the return stroke. The angle of the bottom of the head box to the horizontal should generally be approximately 0, however, some variances, such that the bottom slopes up toward the slice end or down toward the slice end, do not appear to greatly affect the operation of the machine. Similarly, the direction of reciprocation of the head box relative to the horizontal may also be varied to find the optimum for any given machine and material to be processed.

The metering roll 18 governs the thickness of the material extruding from the head box, this roll is rotated at a peripheral speed equal to, or greater than, the speed of the material through the slice 28 to produce a uniform web. In some operations the metering roll 18 may not be an absolute necessity, but is simplifies operation and facilitates the formation of a uniform web.

The wire 20 receives the stock issuing from the slice 28 and travels at a fixed speed relative to the speed of the stock issuing through the slice. Preferably, the speed of the wire will be equal to the speed of the stock through the slice 28 but the wire may move slightly faster or slower to adjust the thickness of the web being laid.

In operation, stock containing sufficient water to provide a consistency of about 6 to 35 percent, preferably about 10 to 20 percent, is metered into the head box 16 by metering valve 14 to maintain the level L substantially constant. The head box is reciprocated to force the stock as a sheet of set thickness determined by the position of the metering roll 18 which rotates at a peripheral speed equal to or greater than the speed of stock through the slice 28 thereby to form a web 32 on the wire 20. The frequency and amplitude of the reciprocation of the head box, and the angles of the reciprocation, and bottom of the head box to the horizontal are adjusted to obtain optimum operation for the specific material being processed. The web 32 is dewatered on the wire 20 and passes through press 34 and dryer 36, and is finally cut to the desired size to form boards.

The following are some specific examples of the instant invention as applied to difierent materials.

EXAMPLE I A mixture of percent perlite, 25 percent reslushed newsprint and 5 percent asphalt on a weight basis was introduced into a Ribbon blender-mixer l0 and fed to a head box 16 operated under the conditions shown in table 1. In this example the angle between the bottom of the head box and the horizontal was 0, and the angle between the line of reciprocation of the head box and the horizontal was l0 so that the head box moved up toward the outlet end.

TABLE 1 Vibration Machine Head box Frequency Amplitud speed consistency (cycles/min.) (111.) (ft/min.) (percent) 700 32 14 1, 275 V8 55 14 1, 400 an 14 1, 440 n 14. 5 s. 5 1, 440 11. 4 12. 1 1, 600 M 16 13 z, 000 M 20 13 2, 400 4 7 17. 7

Boards formed in each of the above runs had similar characteristics to other boards formed using the same feed stock but at the lower conventional consistencies. it will be noted from runs 1, 2, 3 that for given conditions where only frequency is varied an optimum frequency for maximum production can be found.

EXAMPLE II a. A mixture of wood fiber 40% mineral wool 30% binder (starch) 10% other materials (fillers etc.) 20% b A mixture of mineral wool 70% asbestos fiber l% binder (starch) other materials (fillers etc.) 10% c. High yield wood pulp fiber per se The terms stock or fiber-containing stock, as used in the disclosure and claims, do not include as a principal ingredient materials such as nondefibered wood fragments or bark or the like.

Not all fiber mixtures have been described above; the present invention permits the use of more soluble additives since less water is used and thus recovery of such additives is facilitated.

Modifications will be evident to those skilled in the art without departing from the spirit of the invention as defined in the appended claims.

I claim:

1. A method of forming a continuous web of substantially uniform thickness from an aqueous stock containing cellulose fibers and lightweight aggregate while maintaining the homogeneity of the stock comprising; producing said aqueous stock from cellulose fibers, water, and lightweight aggregate, said aqueous stock having a consistency in the range of 6 to 35 percent, maintaining a body of said stock in a head box, subjecting said body to a reciprocating action positively advancing said stock in one direction whereby said stock flows from said head box onto a forming surface, said reciprocating action providing substantially the sole means causing said stock to flow from said head box, controlling the flow of said stock from said head box onto a forming surface thereby to form a layer of controlled thickness on said surface and to produce a substantially uniform thickness web of said stock.

2. A method as defined in claim 1 wherein said consistency is in range of 10 to 20 percent. 

2. A method as defined in claim 1 wherein said consistency is in range of 10 to 20 percent. 